In general, a turbine engine extracts energy from fluid flow. The fluid may be gas, steam, or liquid. One interest in turbine design is to provide high efficiency for energy generation. A turbine typically experiences efficiency loss due to fluid leakage through a clearance gap between a turbine blade and a casing wall in a turbine stage. This gap between the turbine blade tip and the casing is often referred to as a tip gap. The tip gap allows for the blade's mechanical and thermal growth, but the tip gap leakage flow results in a reduction in the work done by the blade and, therefore, the efficiency of the turbine.
Some approaches to improving the turbine efficiency include reducing the tip gap, implementing a more effective tip leakage sealing mechanism, or incorporating passive or active flow control devices. A recent approach to improve efficiency is described in the paper, “Turbine Tip Clearance Flow Control using Plasma Actuators,” by Van Ness II et al. (2006). Van Ness II et al. describes an active flow control device that uses a plasma actuator made up of two metal electrodes separated by a dielectric material mounted on a blade tip The electrodes are formed on the rotor in a single arrangement where EHD principles are used to provide active control of tip clearance flow.
Accordingly, improving turbine efficiency and reducing loss due to tip gap leakage flow is of interest.